1. Field of the Invention
The present invention relates to an illuminator having a linear illuminating area for reading a separated color image using a sensor having a linear reading area.
More particularly, the present invention relates to an illuminator for color separated transmission of illumination light used for an image reading apparatus (referred to as film scanner) in which, for example, an original image of a color positive film is converted into separated color analog signals (such as three prime color image signals RGB) by operating a CCD line sensor to scan, and these signals are processed by an A/D converter for storage as digital data.
2. Related Background Art
Now, in conjunction with FIG. 1 and FIG. 2, a conventional illuminator for reading color separated image using a linear sensor will be described with a film scanner taken as an example.
FIG. 1 is a cross-sectional view showing the layout of a conventional film scanner and FIG. 2 is a perspective view showing the principal part of the structure of the conventional film scanner.
In FIG. 1 and FIG. 2, reference numeral 1a designates a halogen lamp with a mirror, and the cross-section of its irradiating beam is substantially a circle with a luminous distribution of the so-called Gaussian distribution wherein the intensity is greater in the vicinity of the optical axis of the beam and becomes less towards the circumference thereof.
A reference numeral 21 designates an infrared cutting filter, which is provided between a light source 1a and the surface of a filmed original 24 to protect a CCD line sensor 12 from being affected by any infrared light. The original is supported by a supporting frame 9.
A reference numeral 22 designates an uneven illumination correcting filter provided between the light source 12 and the surface of the original 24 in order to make the Gaussian distributed circular irradiation beam an even circular illumination. The uneven illumination correcting filter 22 is such that its density changes gradually by the distance from the center of the optical axis, that is, the density being higher toward the center (the transmissivity is low) and lower toward circumference (the transmissivity is high). Hence the luminous intensity in the circular illumination area is made substantially even.
A reference numeral 23 designates a condenser lens, and 2g designates a filter supporting disc which is a plate substantially in the shape of circle with color separation filters 3, 4, and 5 installed thereon and rotatively structured with an axis 2h as its center. The rotation of the aforesaid filter supporting disc 2g is controlled by a stepping motor 7.
In the case where the original of a color negative film is converted into monochrome, a monochrome conversion correcting filter 6 is provided in order to obtain desirable monochrome image signals by correcting the spectral characteristics of the light source, filmed original, and CCD line sensor. The film supporting frame 9 is movable in the sub-scanning direction by a known transporting mechanism (not shown).
A reference numeral 10 designates a mirror and 11, an image formation lens.
The illuminating light from the halogen lamp la illuminates the filmed original 24 supported by the film supporting frame 9 through the infrared cutting filter 21, color separation filter 3, for example uneven illumination correcting filter 22, and the condenser lens 23.
The optical path is bent by the mirror 10, and the image of the filmed original is formed on the CCD line sensor 12 by the image formation lens 11, and is converted by a photoelectric converter so as to output linear image signals.
When the image signals of the filmed original 24 have been read using the color separation filter 3, by the relative traveling of the CCD line sensor 12 and the filmed original 24, the filter supporting disc 2g is controlled by motor 7 to be rotated to enable the next reading using the color separation filter 4. Then, subsequent thereto, the reading is performed using the color separation filter 5 to complete the readings of the filmed color original.
If the filmed original in color is converted into monochrome image signals, the filter 6 would be selected for the reading operation.
It is possible to employ a photointerrupter for the detection of the reference position of the filter supporting frame, and if a stepping motor is used, the filter can be selected arbitrarily because the step numbers for each of the filters to enter the optical path from the reference position detected by the aforesaid photointerrupter are predetermined.
With a conventional structure such as this, the apparatus is disadantageously large. Particularly, the distance between the light source and the filmed original is long, making it difficult to miniaturize the apparatus.
Also, the illumination for the linear reading area illuminates an area which is not linear, i.e., the circular area with the aforesaid linearity as its center. Therefore, not only the lighting efficiency is low, but it is also difficult to correct the unevenness of the illumination, and there remains the uneven illumination in the area to be scanned by the line sensor.